In a system for providing a video and audio streaming through unicast, in order to implement broadcast-type services where each stream is treated as a TV channel, allocation of bands in a path on which each stream is transmitted and settings for filtering (access control) have been typically performed each time zapping is carried out. As used herein, the term “zapping” refers to channel selection through the user's operation of a remote controller.
For example, for an IPTV service that is implemented through multicast, a band for a core network has enough capacity to deliver all channels at one time. However, a band between each terminal and a station that accommodates terminals is less than or equal to 100 Mbps for current common services. Therefore, if a band that is occupied by one stream is 6 Mbps, then 16 streams at most can be delivered to a terminal through multicast. Many of ADSL (Asymmetric Digital Subscriber Line) systems that are currently in widespread use have an effective performance around 10 Mbps, which can make it difficult to deliver two streams simultaneously. Accordingly, in order to cope with such a band mismatch, it is practical to build a system in the station which transmits a stream alone that the terminal has selected for viewing to the terminal through unicast.
A related art has the disadvantage that when a video and audio stream that is currently being viewed is switched to another video and audio stream through zapping, it takes much time to switch the stream, failing to deliver a zapping performance such as in TV. In particular, a video and audio streaming for which QoS (Quality of Service) is assured, requires additional operations to release the band for the old video and audio stream and to secure the band for a new video and audio stream as compared with the best effort video and audio streaming. This can result in worsening the zapping performance.
FIG. 1 of the accompanying drawings illustrates by way of example a video and audio stream delivery system of the related art.
Delivery server 501 delivers a plurality of video and audio streams to relay means 503 via delivery path 502 through multicast. Terminal 507 transmits a request to deliver a video and audio stream that terminal 507 desires to view and has selected from program information (not shown), to relay means 503 via delivery path 506, band control means 505 and delivery path 504. Relay means 503 transmits a request of a band that is necessary for the delivery in accordance with band information (not shown) of the stream that is requested, to band management means 509 via control line 510. If the requested band can be secured, band management means 509 instructs band control means 505 via control line 508 to secure the band and notifies relay means 503 via control line 510 that the band can be secured. Relay means 503 delivers a video and audio stream requested by terminal 507 to terminal 507 through unicast via delivery path 504, band control means 505 and delivery path 506.
Patent document 1 describes a system having such a configuration. In Patent document 1, in order to speed up the zapping, some of a plurality of video and audio streams that are delivered from a delivery server through multicast, are predicted as streams to be candidates for the next selection, and are delivered to a terminal in advance after they are filtered at the multicast points. Upon receipt of zapping instructions of zapping from a higher level application program and if the prediction comes true, the terminal selects, from among video and audio streams that have been received at the terminal, the relevant video and audio stream(s) and plays back the same.
However, according to the method described in Patent document 1, in addition to the video and audio streams that are currently being viewed by the user, the predicted video and audio streams as well actually flow between the multicast points and the terminal as video and audio streams. Accordingly, network resources are often depleted when network resources between the multicast point and the terminal are not sufficient due to the use of ADSL as described earlier, or when a plurality of terminals receive video and audio streams from the same multicast points. For example, in the case of a line having only a network throughput of 10 Mbps, only one stream of 6 Mbps is allowed to pass through the line. Therefore, speeding up zapping can not be achieved with this method.    Patent document 1: JP2003-143587A